Photoluminescent material of light-emitting diode package structure

ABSTRACT

An LED package structure including a carrier, an LED chip, an encapsulant and a PL material is provided, wherein the LED chip is disposed on the carrier for emitting light. The encapsulant encapsulates the LED chip. The PL material is distributed in the encapsulant. The PL material is suitable for being excited by the light emitted from the LED chip and scattering the light. Moreover, the present invention provides a novel PL material with a molecular formula of W m Mo n (Y,Ce,Tb,Gd,Sb) 3+t+u (Al,Ga,Tl,In,B) 5+u+2v (O,S,Se) 12+2t+3u+3v+3m+3n :Ce 3+ ,Tb 3+ , wherein 0&lt;t&lt;5 and 0&lt;m, n, u, v&lt;15.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of an application Ser. No. 11/160,287,filed on Jun. 17, 2005, now pending, which claims the priority benefitof Taiwan application serial no. 94109063, filed on Mar. 24, 2005. Theentirety of the above-mentioned patent applications is herebyincorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an LED (light-emitting diode) packagestructure. More particularly, it relates to an LED package structurecomprising a photoluminescent diffuser material.

2. Description of the Related Art

As LED luminous efficiency has continued to enhance in recent years,LEDs have gradually replaced fluorescent lamps and incandescent lamps insome applications, such as fast-responding scanner light sources, LCD(Liquid Crystal Display) back light sources, automobile dashboardlighting, traffic lights, and general lighting devices. In comparisonwith conventional light bulbs, LEDs have absolute predominance becauseof features, such as compact size, durability, low voltage/currentoperation, break-resistance, zero heat radiation during illumination, nomercury (and therefore no environmental pollution) and high luminousefficiency (energy saving). In terms of production technologies andapplications today, white LED draws the most attention among LEDs'various lighting colors.

White light is a type of light blended from a plurality of colors oflight. The white light visible to human eyes comprises at least twocolors of light in different wavelengths. For example, blue light andyellow light are blended to form a dual-wavelength white light; or redlight, green light and blue light are blended to form atriple-wavelength white light. Currently white LEDs are fabricated inthree methods. First, there is a so-called triple-wavelength method,wherein an LED chip set is comprised of a red LED chip, a green LED chipand a blue LED chip. Uniform white light is formed by adjustingrespective currents passing through the three chips. This mode featuresa high luminous efficiency along with a higher production cost. Second,there is a so-called dual-wavelength method, wherein an LED chip set iscomprised of a blue LED chip and a yellow LED chip. By adjusting therespective currents of the two chips, uniform white light is formed.This method is characterized in good luminous efficiency and a lowerproduction cost. Additionally, there is a third method, wherein whitelight is formed by blending blue light formed by a blue LED and yellowlight formed by exciting blue light to form yellow phosphor. The thirdmode features a simpler production process, lower luminous efficiencyand a lower cost. Therefore, currently, most white LEDs are based on thethird method. Namely, the white light is formed by means of the bluelight and the yellow phosphor excited by the blue light.

FIG. 1 is a schematic drawing of a conventional white LED packagestructure. In FIG. 1, the conventional white LED package structuremainly comprises package lead pins 100, a blue LED chip 102, an innerencapsulant 104 and an outer encapsulant 106, wherein the blue LED chip102 is disposed on the package lead pins 100 and electrically connectedto the package lead pins 100 via two soldering wires 108; the innerencapsulant 104 comprises yellow phosphor, covering the blue LED chip102; an outer encapsulant 106 is used to cover part of the package leadpins 100, the blue LED chip 102 and the inner encapsulant 104. Theaforesaid white LED uses the blue light emitted by the blue LED chip 102to excite the inner encapsulant 104 to form a dual-wavelength whitelight, which is blended by the blue light and the yellow light.

FIG. 2 is a schematic drawing of another conventional white LED packagestructure. In comparison with FIG. 1, the major improvement of the whiteLED is an additional diffusion layer 110 applied to cover the innerencapsulant 104. The diffusion layer 110 comprises transparent glue inwhich transparent particles or air bubbles are distributed. Thetransparent particles or air bubbles in the diffusion layer 110repeatedly refract the light rays, which enables the tone of the blendedlight to be more uniform.

However, to obtain a better light interfusing effect, the fluorescentpowder on the above-described inner encapsulant 104 and the size anddistributed density of transparent particles or air bubbles in thediffusion layer 110 must be well matched. Since too many factors caninfluence the light interfusing effect, practically it is difficult tosome extent to produce and control the light interfusing effect.

To get a detailed understanding of the above-described LED packagestructure, U.S. Pat. No. 5,998,925 and the ROC patent PN 383508 can beused for reference.

SUMMARY OF THE INVENTION

According, the present invention is directed to provide an LED packagestructure to further enhance the light infusing effect thereof.

According, the present invention is to provide a cold cathodefluorescent lamp, wherein a photoluminescent material (PL material) isused to replace the conventional fluorescent layer and diffusion layerto enhance the light infusing effect thereof.

According, the present invention is to provide a PL material which isdifferent from conventional fluorescent powder but suitable for the LEDpackage structure and cold cathode fluorescent lamps to produce betterlight infusing effect.

The present invention provides an LED package structure, which mainlycomprises a carrier, an LED chip, an encapsulant, and a PL material,wherein the LED chip is disposed on the carrier to emit light rays; theencapsulant is used to encapsulate the LED chip on the carrier; and thePL material is distributed in the encapsulant, wherein thephotoluminescent material is adapted to be excited by the light emittedfrom the LED chip and to scatter the light.

According to one embodiment of the present invention, the carrier is,for example, a printed circuit board (PCB) comprising a chip-holdingcell for disposing the LED chip. The LED chip is electrically connectedto the PCB.

According to one embodiment of the present invention, the carrier is,for example, a package frame. The LED chip is electrically connected tothe package frame via two soldering wires. Besides, the LED chip is, forexample, a blue LED chip.

According to one embodiment of the present invention, the encapsulantcomprises an inner encapsulant and an outer encapsulant, wherein theinner encapsulant encapsulates the LED chip and the PL material isdistributed in the inner encapsulant, and the outer encapsulantencapsulates the inner encapsulant and a part of the carrier.

According to one embodiment of the present invention, the molecularformula of the PL material can be given by:

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,

wherein 0<t<5 and 0<m, n, u, v<15. The aforesaid PL material with saidmolecular formula of:W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15, is a mixture or a sinter. Inaddition, the largest particle diameter is smaller than 30 microns andthe average particle diameter is smaller than 10 microns.

According to one embodiment of the present invention, the PL materialcomprises a fluorescent material and a diffusion material. The particlediameter of the fluorescence material is smaller than 25 microns.

The present invention further provides an alternative cold cathodefluorescent lamp comprising a fluorescent lamp, discharging gas, PLmaterial and an electrode set, wherein the discharging gas is filled inthe fluorescent lamp, the PL material is disposed on the inner wall ofthe lamp and the electrode set comprises an anode and a cathode with theanode disposed at one end of the light tube and the cathode disposed atthe other.

According to one embodiment of the present invention, the molecularformula of the PL material can be given by:

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15. The PL material with the molecularformula ofW_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15 is a mixture or a sinter. In addition,the PL material comprises a fluorescent material and a diffusionmaterial adhered by the fluorescent material.

The present invention also provides an alternative PL material. Themolecular formula of the PL material can be given by:

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15. Moreover, the PL material with themolecular formula ofW_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15, can be a mixture or a sinter.

The present invention uses a PL material to replace the conventionalfluorescent layer and diffusion layer for light conversion and a lightinterfusing effect. Thus, there are no more match problems among thevariants in the prior art, such as the materials of the fluorescentlayer and diffusion layer, the particle size and the particledistribution density, and the like. Besides, the overall procedure forfabricating LED packages is effectively simplified along with a lowerproduction cost and better light interfusing effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a schematic drawing of a conventional white LED packagestructure.

FIG. 2 is a schematic drawing of another conventional white LED packagestructure.

FIG. 3 is a schematic drawing of a white LED package structure accordingto a first embodiment of the present invention.

FIG. 4A and FIG. 4B are schematic diagrams showing a PL material.

FIG. 5A and FIG. 5B are schematic diagrams showing an alternative PLmaterial.

FIG. 6 and FIG. 7 are schematic drawings of white LED packages structureaccording to a second embodiment of the present invention.

FIG. 8 is a schematic drawing of a cold cathode fluorescent lampaccording to a third embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS The First Embodiment

FIG. 3 is a schematic drawing of an LED package structure according tothe first embodiment of the present invention. In FIG. 3, the LEDpackage structure in the first embodiment of the present inventionmainly comprises a carrier 200, an LED chip 210, an encapsulant 220 anda PL material 230, wherein the LED chip 210 is disposed on the carrier200 to emit light; the encapsulant 220 encapsulates most of the carrier200 and the LED chip 210 thereon; and the PL material 230 is evenlydistributed in the encapsulant 220. The PL material layer 230 issuitable to be excited by the light emitted from the LED chip 210 and toscatter the light.

In the first embodiment, the carrier 200 is, for example, package leadpins 200′ as shown in FIG. 3. The package lead pins 200′ comprise afirst lead pin 202 and a second lead pin 204. On the top of the firstlead pin 202 is a carrier pad 206, comprising a chip-holding cell 208.The chip-holding cell 208 is of a concave shape suitable to hold the LEDchip 210.

The LED chip 210 is disposed in the chip-holding cell 208 of the carrierpad 206 to emit light. In the first embodiment, the LED chip 210 is, forexample, a blue LED chip. The surface of the LED chip 210 has electrodes212, comprising a cathode and an anode, wherein the cathode iselectrically connected to the first lead pin 202 and the anode to thesecond lead pin 204 respectively via soldering wires 209 a and 209 b.

The encapsulant 220 is used to encapsulate a portion of the package leadpins 200′, the LED chip 210, the PL material 230, and the solderingwires 209 a and 209 b. The first lead pin 202 and the second lead pin204 protrude from the bottom of the encapsulant 220. The encapsulant 220comprises an inner encapsulant 222 and an outer encapsulant 224, whereinthe inner encapsulant 222 encapsulates the LED chip 210, and the outerencapsulant 224 encapsulates the inner encapsulant 222 and a portion ofthe carrier 200.

Note that the PL material 230 in the present invention is uniformlydistributed in the inner encapsulant 222. The PL material 230 serves asboth a fluorescent layer and a diffusion layer of the prior art. Thatis, the PL material is not only excited by the light emitted from theLED chip 210, but is also capable of scattering the light. As a result,the light emitted from the LED chip 210 and the light formed by excitedPL material 230 are blended more uniformly to further achieve a betterlight interfusing effect. The PL material 230 is not limited to theapplication of the inner encapsulant 222 in the first embodiment. The PLmaterial 230 is also applicable to other package, structure or lightingswhich are based on the excited phosphor to produce light. In all ofthese applications, a good light interfusing effect can be achieved.

FIG. 4A and FIG. 4B are schematic diagrams showing a grain of the PLmaterial. In FIG. 4A and FIG. 4B, the grain of the PL material 230comprises a fluorescent material 230 a and a diffusion material 230 badhering to the fluorescent material 230 a which is distributed in thediffusion material 230 b. As the incident light emitted from the LEDchip 210 enters the PL material 230, the fluorescent material 230 ainside the PL material 230 is excited and produces a light in otherwavelength. Besides, the diffusion material 230 b scatters the lightonto other grains of the PL material 230, enabling the LED packagestructure to produce a better light interfusing effect. In FIG. 4B,there is a transitional-phase 230 c embracing the fluorescence material230 a. The transitional-phase 230 c may produced in certain conditionwhen fabricating the PL material 230.

In the first embodiment, the molecular formula of the PL material 230can be given by:

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15. In FIG. 4A, to achieve a better lightinterfusing effect, the largest particle diameter of PL material Dmax issmaller than 30 microns, the average particle diameter thereof issmaller than 10 microns, and the particle diameter of fluorescentmaterial Di is smaller than 25 microns. Moreover, the PL material withthe molecular formula of

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,

0<t<5 and 0<m, n, u, v<15, can be a mixture or a sinter.

FIG. 5A and FIG. 5B are schematic diagrams showing a grain of analternative PL material 230. In FIG. 5A and FIG. 5B, the grain of the PLmaterial 230 comprises a fluorescent material 230 a and a diffusionmaterial 230 b. The difference between FIG. 5A and FIG. 5B is that thediffusion material 230 b of the PL material 230 is distributed in thefluorescent material 230 a. The alternative PL material 230 can alsoachieve the same light interfusing effect.

It is known to those skilled in the art that the disclosed PL material230 is not limited to the aforesaid package structure. In fact, thedisclosed PL material 230 is also applicable to any package structurebased on the excited-phosphor mode to produce light. To reach the goal,the original fluorescent layer needs to be replaced by an innerencapsulant 222 and a PL material 230 distributed therein.

The Second Embodiment

FIG. 6 and FIG. 7 are schematic drawings of white LED package structuresaccording to the second embodiment of the present invention. In FIG. 6,the structure in the second embodiment is similar to that of the firstembodiment. The difference in the second embodiment is that the carrier300 therein is a printed circuit board (PCB) 300′ on which the packageis disposed.

The LED package structure in the second embodiment mainly comprises aPCB 300′, an LED chip 310, an encapsulant 320 and a PL material 330. Theencapsulant 320 similarly comprises an inner encapsulant 322 and anouter encapsulant 324, wherein the inner encapsulant 322 encapsulatesthe LED chip 310, and the outer encapsulant 324 encapsulates a portionof the PCB 300′, the LED chip 310, the inner encapsulant 322, the PLmaterial 330 and the soldering wires 314. When the encapsulant 320comprises only an outer encapsulant 324 without the inner encapsulant322, the outer encapsulant 324 can only comprise the PL material 330.

The LED chip 310 is disposed on the PCB 300′. Connection pads 302 andelectrodes 312 are disposed on the PCB 300′ and the LED chip 310,respectively. The electrodes 312 are connected to the connection pads302 on the PCB 300′ through two soldering wires 314, so that the PCB300′ is electrically connected to the LED chip 310.

The inner encapsulant 322 is disposed on the PCB 300′ and covers theaforesaid LED chip 310. The PL material 330 is uniformly distributed inthe inner encapsulant 322 and comprises a fluorescent material and adiffusion material adhering to the fluorescent material. When theincidence light from the LED chip 310 enters the PL material 330, thefluorescent material therein is excited and produces a light with adifferent wavelength. The diffusion material scatters the light ontoother particles of the PL material to produce a better light interfusingeffect. In the second embodiment, the molecular formula of the PLmaterial 330 can be given by:

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15. To achieve a better light interfusingeffect the largest particle diameter of the PL material 330 Dmax is,similarly, smaller than 30 microns, the average particle diameterthereof is smaller than 10 microns, and the particle diameter offluorescent material Di is smaller than 25 microns. Moreover, the PLmaterial with the molecular formula ofW_(m)Mo_(n)(Y,Ce,Tb,Gd,Sc)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15, can be a mixture or a sinter.

In FIG. 7, to enhance the light-condensing effect of the LED packagestructure, a chip-holding cell 304 is disposed in the PCB 300′. Thechip-holding cell 304 is of a concave-cup shape suitable for holding theLED chip 310. Moreover, a reflecting-film layer can be plated on thesidewall of the chip-holding cell 304 as an option of increasing thelight-reflection effect.

The Third Embodiment

In the first and second embodiment of the present invention, the PLmaterial is used in the LED package structure. In addition, the PLmaterial can also be used in general cold cathode fluorescent lamps toachieve a better light interfusing effect.

FIG. 8 is a schematic drawing of a cold cathode fluorescent lampaccording to the third embodiment of the present invention. In FIG. 8,the cold cathode fluorescent lamp 400 comprises a light tube 410, adischarging gas (not shown in the figure), a PL material 420 and anelectrode set 430, wherein the light tube 110 is properly filled withdischarging gas, such as mercury vapor and inert gas. The PL material420 is applied on the inner wall of the light tube 410. In addition, theelectrode set 430 comprises both an anode and a cathode individuallydisposed at two ends of the light tube 410, respectively. The electrodeset 430 is electrically connected to a power supply (not shown in thefigure).

When a bias voltage is applied to the electrode set 430, the discharginggas in the light tube, such as the mercury vapor and the inert gas, isexcited to an excited state, then returns to a steady state. While thedischarging gas returns to the steady state, the gas releases energy byemitting an ultraviolet light. With the aforesaid mechanism, when theultraviolet light released by the discharging gas reaches the PLmaterial 420 on the wall of the light tube 410, the PL materialcomprising the fluorescent material and the diffusion material adheringto the florescent material emits a visible light to achieve lightingeffect. Meanwhile, the diffusion material adhering to the fluorescentmaterial scatters the light to produce a better light interfusingeffect. The limitations of the PL material molecular formula and theparticle size are the same as described in the first and secondembodiment, so it is not repeated.

To sum up, in the LED package structure of the present invention, theaforesaid PL material is used to replace the fluorescent layer and thediffusion layer of the prior art. The molecular formula of the PLmaterial 330 can be given by:

W_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,

wherein 0<t<5 and 0<m, n, u, v<15. The PL material is not only excitedby the light emitted from the aforesaid LED chip, but also scatters thelight. Thus, the light emitted from the LED chip and the light excitedby the PL material are blended more uniformly to achieve a better lightinfusing effect.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the specification andexamples to be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims andtheir equivalents.

1. A photoluminescent material with a molecular formula ofW_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15.
 2. The photoluminescent material ofclaim 1 with the molecular formula ofW_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15, is a mixture.
 3. The photoluminescentmaterial of claim 1 with the molecular formula ofW_(m)Mo_(n)(Y,Ce,Tb,Gd,Sb)_(3+t+u)(Al,Ga,Tl,In,B)_(5+u+2v)(O,S,Se)_(12+2t+3u+3v+3m+3n):Ce³⁺,Tb³⁺,wherein 0<t<5 and 0<m, n, u, v<15, is a sinter.